Hand trucks, and more specifically collapsible or folding hand trucks, are generally known in the art. It is desirable for such trucks to be collapsed into as small and lightweight a form as possible, while still providing a sturdy uncollapsed truck that is capable of handling heavy loads. Additionally, it is desirable to design the truck so that bulky and odd-shaped objects can be easily accommodated. At times, these goals produce incompatible design efforts that are difficult to effectively reconcile.
For example, U.S. Pat. No. 3,102,648 describes various embodiments of a collapsible hand truck in which objects being moved by the device are not balanced upon two wheels, but are instead placed on three or more castor wheels (similar to a cart). One embodiment of the device is collapsible by rotating a bottom member (28, 30) aftward about a lower horizontal axis of rotation. This design appears to be strong during use, but is bulky when collapsed.
The same is true for U.S. Pat. No. 3,193,123, which describes a hand truck having an extension E that is rotatably connected to a frame F at an axis of rotation distinct from the axis of rotation of a pair of wheels W. Secondary wheels S are attached along the upper rear side of the frame F. When the extension E is rotated downward, it rests upon a toe plate T. Both the toe plate and extension may be used to support heavy loads. Alternatively, the hand truck may be rotated 90.degree. such that the frame is horizontal and the secondary wheels S are in contact with the ground. In this orientation, a load may be placed on top of the frame and the extension may act as handles.
U.S. Pat. No. 4,235,449 describes a hand truck capable of collapsing into a step stool. The hand truck includes a foot 18 as well as an extension bed 44. The extension bed is rotatably connected along the inside of frame side rails 12 at an axis of rotation distinct from the axis of rotation of a pair of wheels 42. This design appears to be sturdy, but the forward location of the bed in the collapsed state prohibits the steps 14 from being flush with the side rails 12.
U.S. Pat. No. 4,286,796 is missing its drawing sheet 2 of 2. This is not due to an error of our searcher, but instead reflects a misfiled drawing at the U.S. Patent and Trademark Office. Using only drawing sheet 1 of 2 (and the written text), it appears that the '796 patent describes a collapsible hand truck in which a lower platform 15 is upwardly rotatable about the axis of rotation of the wheels. A cross bar 33 prohibits the platform 15 from extending past a generally horizontal orientation. Spring hoops 35, 36 squeeze the arms 31, 32 of the platform 15 against the frame 11, thus holding the platform firmly in position when it is fully extended.
U.S. Pat. No. 4,299,403 describes a foldable luggage carrier having a lower platform 14 rotatably connected to the inside of a main frame 10. A bottom section 44 (i.e., stop) is provided to support the platform and prevent it from rotating downward more than roughly 90 degrees. To collapse, the platform is rotated forward about an axis of rotation at a pair of wheels 16.
U.S. Pat. No. 5,549,317 describes a foldable hand truck having a telescopically extendible handle 18. A load support plate 64 is rotatably connected to the lower end of a main support assembly 14. A luggage support frame 62 is additionally provided between the main support assembly 14 and the load support plate 64. Both the luggage support frame 62 and the load support plate 64 are pivoted upward to reach the folded state. These components are rotated about an axis of rotation distinct from the axis of rotation of the wheels.
While the above patents describe collapsible or folding hand trucks, they are not particularly compact as well as sturdy. Additionally, none of the prior art devices above describe a hand truck having a bottom frame that provides numerous angular positions of the bottom frame with respect to the back frame. This attribute is highly desirable with loads that are bulky or oddly shaped. Thus, a need exists for a folding hand truck that is conveniently configurable between its in-use position and a storage position where the storage position is extremely low profile, while the in-use position is strong, sturdy, and capable of handling heavy and bulky loads. The present invention is directed to fulfilling this need.